1. Field of the Invention
This invention relates generally to apparatuses and methods for configuring an optical signal transmission system. More particularly, this invention is related to a dynamic gain equalization device and method of configuring a dynamic gain equalization system in an optical communication network applying an adaptive spectrum decomposition technique.
2. Description of the Related Art
The wavelength division multiplexing (WDM) is an emerging technology that enables service providers to significantly increase transport capacity while leveraging existing fiber-optic equipment. Application of erbium-doped fiber amplifiers (EDFAs) to amplify the optical signals in an optical communication system is a key enabling technology for WDM communications. Signal amplification technologies provide the necessary gain to overcome fiber attenuation across all information channels. Due to non-periodic changes in the power of input channels caused by channel add-drop operations, network reconfiguration, fiber cuts, or packetized traffic, the gain excursion in an EDFA leads to the occurrence of wide time-variant swings in the output power and output optical signal-to-noise ratio (OSNR). Moreover, the gain of an EDFA is, in general, wavelength-dependent, which leads to different gains among WDM channels. Hence, signals traversing a cascade of several amplifiers will experience an increasing OSNR spread among channels. In order to tackle the degradation of OSNR, dynamic gain equalizers are required in next generation wide-band optical communication system.
Therefore, a need still exists in the art in the field of the optical signal transmission systems to provide a dynamic gain equalization devices and configuration to overcome such difficulties and limitations. It is desirable that such device and system configuration can achieve effective equalization with simple and conveniently controllable configuration such that signal equalization process can be accurately performed with simplified processes.
Therefore, it is an object of the present invention to provide new and improved configuration and methods for configuring a dynamic gain equalization to minimize the wavelength dependent gain variations among different channels and to reduce the optical signal-to-noise spread over several channels such that the problems and difficulties as encountered in the prior art may be resolved.
Specifically, it is an object of this invention to provide optical gain equalization devices applying the techniques of adaptive spectrum decomposition. The optical signal to be equalized is first adaptively decomposed into a series of narrowly spectrum-banded sub-signals and a residual signal. The spectrums of these sub-signals are roughly mutually exclusive while in combination; these sub-signals dynamically cover the portions of the original signal spectrum where power equalizations are required. The combination of all the sub-signal spectrums plus the residual signal spectrum substantially covers the entire spectral range of the original optical signal. The adaptive spectrum decomposition is implemented with tunable filters arranged as a cascade array. In a preferred embodiment, the cascade array may be implemented with optical micro-electromechanical system (MEMS) filters or tunable arrayed-waveguide gratings (AWG) filters.
Another object of this invention is to use of tunable filters in place of fixed filters to adaptively carry out the spectrum decomposition thus requiring less number of filters and provide better scalability. Another object of this invention is to implement variable optical attenuator array manufactured with MEMS technology and controlled by a VOA array driver such that convenient and effective control can be accurately performed to generate equalized output signals.
Briefly, in a preferred embodiment, this invention discloses an optical gain equalization system for receiving and equalizing a multiple-channel input optical signal. The optical gain equalization system includes a cascaded array of tunable optical filters filtering the multiple-channel input optical signal and generating a plurality of sub-signals plus a residual signal and each of the sub-signals transmitted over a mutually exclusive filter-specific spectrum-range while a combination of all the filter-specific spectrums together with the residual signal spectrum substantially covering the entire spectral range of the multi-channel input optical signal. The gain equalization system further includes a corresponding array of variable optical attenuators (VOAs) each connected to one of a corresponding tunable optical filter for attenuating the sub-signal transmitted over the filter-specific spectrum range for generating an equalized sub-signal. And, the gain equalization system further includes a multiplexing means for receiving and multiplexing the equalized sub-signals generated by the array of variable optical attenuators (VOAs) and the residual signal for generating an equalized output optical signal.
This invention further discloses a method for receiving and equalizing a multiple-channel input optical signal. The method includes the steps of: A) dynamically analyzing the multi-channel input optical signal for generating a set of signal spectral data. B) employing the set of signal spectral data for adaptively decomposing the multi-channel input optical signal into decomposed sub-signals plus a residual signal. And, C) employing the set of signal spectral data for dynamically equalizing the sub-signals to generate equalized sub-signals. In a preferred embodiment, the method further includes a step of employing an automatic equalization system controller to receive and apply the set of signal spectral data to control the steps of adaptively decomposing the multi-channel input optical signal into decomposed sub-signals plus a residual signal and the step of dynamically equalizing the sub-signals to generate equalized sub-signals.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment which is illustrated in the various drawing figures.